Web temperature control apparatus



Jan. 3, 1967 w, STELLING, JR" ET AL 3,295,842

WEB TEMPERATURE CONTROL APPARATUS 2 SheetsSheet 1 Original Filed March15, 1961 IN VEN TORS BY m t ATTORNEYS Jan. 3, 1967 w. R. STELLING, JR.ETAL 3,295,842

WEB TEMPERATURE CONTROL APPARATUS Original Filed March 15, 1961 2Sheets-Sheet 2 BY nut/07M ATTORNEYS United States Patent 3,295,842 WEBTEMPERATURE CONTROL APPARATUS Walter R. Stelling, Jr., Wauwatosa, Wis.,and Frederick H. Wittel, Cincinnati, Ohio, assignors to Faustel, Inc.,Milwaukee, Wis., a corporation of Wisconsin Original appiication Mar.15, 1961, Ser. No. 96,026, now Patent No. 3,163,406, dated Dec. 29,1964. Divided and this application Aug. 8, 1963, Ser. No. 300,878 1Claim. (Cl. 2633) This invention relates generally to drying ovens forwebs and relates more particularly to temperature control systems forsuch webs.

This application is a divisional application of US. Serial No. 96,026filed March 15, 1961 which issued as Patent No. 3,163,406 on December29, 1964.

In equipment of the type to which the present invention relates, it isimportant to be able to accurately control the temperature of the webto'prevent web damage by temperatures which are too high, and on theother hand, to insure sufiicient heat to properly dry the web.

Many factors affect the drying effect of the web for any setting of theoven, for example, varying moisture content or different web speeds. Itis imperative to be able to immediately change the heat input to therapidly moving web so as to provide the proper drying effect withoutdelay and without casing the control mechanism to hunt.

Shortcomings of conventional drying systems include their tendency tohunt in attempting to establish the proper web temperaturea slight blastof heat causing excessive web temperature rise. Other conventionalsystems use web temperature sensing devices which in themselves givefalse or inaccurate temperature readings, due in some cases, to the heatof friction developed by the moving web in contact with the sensingdevice.

Accordingly, the present. invention provides. a web temperature sensingdevice which will accurately measure the temperature of the web as thelatter leaves the drying oven and without contacting the web.

More specifically, the invention provides an improved thermocouple andbolder therefor by means of which the sensing end of the thermocoupleaccurately senses the web temperature and can be precisely adjustedrelative to and protected from the rapidly moving web.

These and other objects and advantages will appear herein as thisdisclosure progresses, reference being had to the accompanying drawings,in which:

FIGURE 1 is a schematic diagram of a web drying oven assembly and acircuit diagram of the web temperature control system in accordance withthe present invention;

FIGURE 2 is a perspective view of the thermocouple unit shown in FIGURE1, but on an enlarged scale and with parts broken away and in sectionfor clarity in the drawings;

FIGURES 3 and 4 are plan and side elevational views of the contactlesssensitive instrument means for use in the circuit shown in FIGURE 1;

FIGURE 5 is an enlarged detail view of the loop end of the thermocouplemade in accordance with the present invention; and

FIGURE 6 is a schematic external wiring diagram of the motor operator.

Oven

Referring in greater detail to the drawings, the drying oven 0 is of theenclosed tunnel type having an exhaust conduit 6 extending from adjacentthe entry end of the tunnel. A series of blast tubes 7 extend inside thetunnel and across its width and act to produce a direct and localizedblast of air on the web W as it moves rapidly through the tunnel on theidler rolls 8 and in the direction indicated by the arrow in FIGURE 1.The supply conduit 9 furnishes heated air to one end of each of thetubes from the heating chamber C in which is located the burner B, to bedescribed. If a more complete description of the structure and functionof the blast tubes or oven is deemed necessary or desirable, referencemay be had to the co-pending United States patent application, SerialNo. 52,117, filed August 6, 1960, and entitled, Web Dryer, which issuedon January 22, 1963, as US. Patent No. 3,074,179.

Air supply A fan F is provided for forcing air past the burner B,through conduit 9, out of the tubes 7 and over the surface of the Web.In the illustration shown, the burner is located on the pressure side ofthe fan F but of course the burner could also be located on the suctionside of the fan. The air supplied by the fan is preferably filtered andmay consist of fresh air mixed with some of the air which has beenexhaustedfrom the oven 0. In other words, the system may be of therecirculating or nonrecirculating-type, with the burner located on thesuction or pressure side of the circulating fan.

Fuel Valve Means are provided for furnishing a properly proportionedmixture of airand fuel to the burner. This means consists of aconventional mixing or ratio valve mechanism V having an air inletopening 10 and a fuel supply conduit 11 for supplying fuel such as gasto the valve mechanism. The valve mechanism is located on the inlet sideof the blower 12, and the gas and air are intimately mixed and thendelivered by blower 12 through its outlet conduit 12a to the burner.These ratio valves are conventional and may be of the type shown inUnited States Patent No. 2,286,173, issued June 9, 1942, and furtherdescription of them is not believed to be necessary except to say thatthe valve mechanism serves to vary the volume of air as received from asupply source at any pressure, and to vary the volume of fuel asreceived from a supply source at any pressure, and to modify theproportioning so obtained, and to establish such modification fordifferent stages of the feed fiow of the proportioned air and fuel; bysuch facility, the combustible mixture ultimately resultant from saidproportioning, being of consistency which is dictated by the conditionsunder which the burner is operated. In short, the valve mechanism isopened or closed to vary the amount of fuel by a linkage L to therebyvary the heat delivered by the burner.

Fuel valve adjusting means Means are also provided for actuating thelinkage L and this means may take the form of a motor operator MO whichincludes an electric shaded coil motor M having a rotatable shaft 14. Alink 15 is secured to one end of the shaft 14 and is connected withlinkage L for operation thereof. An adjustable resistor or potentiometercarried' by the motor has a wiper or slider 15a secured to the other endof shaft 14. The motor M of the operator is driven in either direction,and is connected by wires 16, 17, and 17a to a relay R of theproportional position control PPC, as will more fully appear. Thedirection of rotation of the motor shaft 14 is determined by the relay Rof the control apparatus to be described, and the shaft is caused torotate in one direction to thereby open the valve mechanism V thedesired amount for more heat; and in the opposite direction to close thevalve mechanism V the desired amount through the linkage L. The motoroperator MO is also of conventional design may be of the typemanufactured by Barber-Colman Company of Rockford, Illinois.

Proportionate position control A proportional position control PPCserves to position the shaft 14 of the motor M in proportion to atemperature change as sensed by a thermocouple T connected by conductorsT1 and T2 to the control PPC. The proportional position control PPC maybe of the type manufactured by Wheelco Division of Barber-Colman Companyand as shown in Patent 2,228,163, issued January 7, 1941, and enables avacuum tube oscillator to control a relay without requiring theengagement of contacts for controlling the oscillator. This control mayutilize a relay such as shown in Patent 2,443,784, issued June 22, 1948,and a brief description of the control PPC will follow which is believedsufficient for purposes of this disclosure.

The apparatus and circuit shown in FIGURE 1 comprises; an oscillatorcircuit OS including an electron discharge gun in the form of a vacuumor oscillator tube OT, a grid leak and condenser LC in the input or gridcircuit of tube OT, tuning or pick-up coils 19 and 20, and the outputcircuit of tube OT may be supplied from a battery 21; contactlesssensitive instrument means CS to be presently described for affectingthe oscillator circuit; and an electro-responsive device such as a relayapparatus R controlled by the oscillator output change for controllingthe temperature to which the contactless sensitive means CS isresponsive. In order to effect operation of the polarized relay R inresponse to changes in the plate current of the oscillator circuit OS, arepeater or amplifier tube AT is provided. The load impedance I iscommon to both the output circuit of the oscillator tube and the inputcircuit of the repeater tube, the latter circuit extending through thepotentiometer P which is connected across a suitable bias battery BB.Also included in the circuit are a radio frequency choke coil CC, aninductance IN, and a variable condenser VC. A by-pass condenser BPC islocated in the by-pass circuit which together with the choke coil CCprevents the flow of high frequency oscillatory currents through theload impedance I and the battery 21, only the non pulsating component ofthe plate current flowing through the load impedance and the battery.

The output circuit of the tube AT is energized from a suitable battery21a and extends to the Winding WR of the relay R. Energization of thewinding operates the moveable contact of the relay.

The motor M of the motor operator MO is connected to a source of energythrough conductors 23, 24. The motor is also connected to theproportionate position control by Wires 16, 17, and 17a. Morespecifically, wires 16 and 17 are connected to the contacts of relay R,and wire 17a is the ground. As shown in FIGURE 6, the ground line 17a isconnected to the terminal X of the terminal block TB of the motor, andlines 16 and 17 to terminals 2 and 3 respectively. The direction ofmotor rotation depends, of course, on the position of the relay switch,and when a circuit is formed between points X and 2 of the block, themotor rotates in one direction; when the circuit is through points X and3, motor rotation in the opposite direction occurs. Thus, operation ofthe relay effects corresponding operation of the motor M and the motoroperator to control the fuel valve V, previously described.

The contactless sensitive means CS includes a setting pointer 18 whichis manually set along a temperature scale S at the pre-determinedtemperature at which it is desired to hold the web. Secured to thesetting point 18 are the pair of oscillator pick-up coils 19 and 20between which flows an oscillating current. The frequency of thisoscillating current is changed when a metal flag 20' mounted on atemperature indicating pointer arm 22 is moved between the coils by theslightest temperature change as sensed by the thermocouple T. That is tosay, the sensing thermocouple T develops a millivoltage and M to bedriven in one direction or the other.

causes the indicator flag to swing between the pre-positioned oscillatorpick-up coils. More specifically, fluctuations of web temperature affectthe thermocouple T so as to vary the energization of the winding 25,whereby fluctuations in temperature are converted into correspondingmovements of the arm 22, pivoted at 22a and its flag 20, movement of thefiag being effective through the circuit shown cause the relay windingto open or close the contacts of relay R, and thus actuate the motor Mto control the heat input of the burner B. Stated otherwise, the outputof the oscillator circuit varies depending on the position of the flagin the coils and is fed to the polarized relay R.

As previously mentioned, the relay R causes the motor An adjustableresistor or slider 15a fixed on the end of the motor shaft 14 is thusdriven to match the oscillator output to the polarized relay. Statedotherwise, the resistor 15a is rotated until it picks off the samevoltage as the output of the proportionate position control PPC.

Thus, as the motor shaft 14 rotates, the process input will beproportioned depending on the relative position of the setting pointer18 and the indicator arm 22. Thereby, in this modified bridge typecontrol circuit, a change in web temperature causes an electricalunbalance of the polarized relay, and this unbalance causes the motor Mof operator M0 to rotate in one direction or the other andcorrespondingly to move the valve mechanism V in a direction to restorethe web temperature toward the pre-determined value and bring theelectrical bridge into balance.

Thermocouple and holder The novel thermocouple will now be described indetail as well as the novel means for mounting it and sensing thetemperature of the web.

The web moves through the oven at high rates of speed, for example,speeds of 200 to 600 feet per minute are not uncommon. An air stream orair curtain is developed along the surfaces of the web and moves alongwith it. This curtain is in the nature of one-eighth of an inch inthickness and clings tightly to the web surface. In other words, thereis a Stratification of air adjacent the surface of the web which hangson to the web and moves along with it. It is this curtain of air thatprovides a good medium for sensing the temperature of the web becausewhen the web leaves the oven after traveling a considerable distancethrough it, the air curtain is at the same temperature as the webitself.

The thermocouple T is positioned accurately and closely adjacent to thesurface of the web within the air curtain, and adjacent the dischargeend of the oven. By positioning the end or hot juncture of thethermocouple at a distance of approximately one-thirty second of an inchfrom the web surface, accurate temperature readings of the web itselfcan be made.

A holder H is provided for precisely locating the thermocouple inadjustable relationship to the web surface to thereby pick up the webair-skin temperature. This holder consists of a fiber block base member26 having two opposite sides 27 and 28 secured thereto and which havetheir free edges positioned closely adjacent the web surface. A rearwall 29 also extends from the base member 26 to closely adjacent the websurface. The extreme end of the thermocouple is formed as a loop, oneportion of the loop being constituted of a metal such as constantan 30and another portion of the loop being constituted of a metal such asiron 31. Both of these metals are joined together to form a hot junction32 where the temperature is actually sensed. By forming these two wiresto define a loop, a much more accurate sensing of the web is obtained.In other words, by forming a flat loop and having it positioned parallelto the web, the wires cover a greater portion of the width of the Weband a more accurate reading is obtained at the hot juncture 32.

The loop is also positioned so that it extends in a direction in whichthe Web is traveling so that it will not be bent, twisted or otherwisedamaged if it is accidentally touched by the rapidly moving web.

As indicated, it is also necessary to precisely locate this looprelative to and closely adjacent the web, and for this purpose a coarseadjustment and a fine adjustment are provided as follows. A threadedfitting 34 is securely engaged in the base member 26 and a tube 33extends through the fitting and contains the wires T1 and T2 of thethermocouple. An adjustable nut 37 in threaded engagernent with fitting34 acts to compress a double beveled ferrule 35 located on the tube.Thus, a pressure fitting is formed for the tube and allows the tube tobe adjusted relative to the fitting 34 to provide the coarse adjustment.The fine adjustment for locating the thermocouple precisely relative tothe web is provided by the set screw thread connection 38 between theholder H and the bracket 39 by means of which the holder is mounted onthe oven.

It is necessary to prevent the web from fluttering and for this purposea roller 40 is positioned under the web and immediately under thethermocouple. It will be noted the extreme end of the thermocouple islocated within the substantially enclosed chamber 41 formed by the basemember and the three sides 27, 28, and 29. The air curtain rushing alongwith the web enters the chamber 41 via the opening 42 in the front sideof the holder H. With this particular holder and thermocouplearrangement, and the shape of and proximity of the thermocouple loop endto the web, the thermocouple is very accurate in sensing the temperatureof the web. The fiber block is a poor heat conductor which minimizesheat dissipation from the holder.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claim particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention:

In a web dryer oven having a discharge end from which the rapidly movingand dried web emerges, a thermocouple holder secured on the outside ofsaid oven and adjacent said end, said holder comprising, a base memberadapted to be rigidly positioned adjacent a surface of said web, atleast two opposite side walls extending generally in the direction ofweb movement and also a rear wall, all walls extending downwardly fromsaid base member and towards said web and having free edges positionedclosely adjacent said web, said base member and said walls together withsaid web defining a substantially enclosed chamber having a front side,unobstructed opening for an air curtain moving along with said web, saidfront side opening facing in the direction from which the web approachessaid holder, a thermocouple secured on said holder and having a free endcomprised of a fiat loop and located in said chamber and closelyadjacent to and parallel with said web, means for adjusting said holderrelative to said web, and means for adjusting said thermocouple relativeto said holder and web.

References Cited by the Examiner UNITED STATES PATENTS 2,279,846 4/1942Stapleton 136221 2,627,182 2/1953 Quereau et al 73351 2,668,701 2/1954Dietrich 263-3 2,872,173 2/1959 Munker 2633 2,991,654 7/1961 Engelhard73--351 X FREDERICK L. MATTESON, 111., Primary Examiner. D. A. TAMBURRO,Assistant Examiner.

